text: A Curtin–Hammett scenario was invoked to explain selectivity in the syntheses of kapakahines B and F, two cyclic peptides isolated from marine sponges. The structure of each of the two compounds contains a twisted 16-membered macrocycle.
  A key step in the syntheses is selective amide bond formation to produce the correct macrocycle. In Phil Barans enantioselective synthesis of kapakahines B and F, macrocycle formation was proposed to occur via two isomers of the substrate. The more easily accessible, lower energy isomer led to the undesired product, whereas the less stable isomer formed the desired product. However, because the amide-bond-forming step was irreversible and the barrier to isomerization was low, the major product was derived from the faster-reacting intermediate. This is an example of a Curtin–Hammett scenario in which the less-stable intermediate is significantly more reactive than the more stable intermediate that predominates in solution. Because substrate isomerization is fast, throughout the course of the reaction excess substrate of the more stable form can be converted into the less stable form, which then undergoes rapid and irreversible amide bond formation to produce the desired macrocycle.  This strategy provided the desired product in >10:1 selectivity. (I think theres an error in the Scheme. See Talk pages.)